I created a quick Flash banner to test BE. The swf file’s dimensions are exactly the same as standard twenty fourteen header – width=1260 height=240. The banner works ok, but somehow the div #site-header box changes to 1260×246 causing a 6px strip of whitespace below the banner (the background is white).
I am working with child of twenty fourteen but have only made a few css changes from out-of-the-box twenty fourteen.
If I swap back to a WP default header image (1260×240), then the div works and there’s no whitespace problem.